Phase modulation



0a. 6, 1942. M. G. CROSBY 2,298,092

PHASE MODULATION Original Filed Oct. 6, 1938 2 Sheets-Sheet 2 was; 5 FREQMUUZ SH/FiZ-R AND OR 44mg.

\ 38 L/MITERAA/D 0/? 34 AMPLIFIER 36' CARR/ER l SOURCE PHASE R. E amass S/l/FIZ-R c0/v0-sRs FREQUENCY Ml/ZT/Pl/ER,

I- 44/0 0R AMPUI'UDE L/M/TER 4w 36' 0R AMPLIFIER ATTORNEY Patented Oct. 6, 1942 PHASE MQDULATION Riverhead, N. Y., assignor to Radio Corporation of America,

Murray G. Crosby,

of Delaware a corporation Application October 6, 1938, Serial No. 233,539, now Patent No. 2,250,296, dated July 22, 1941, which is a division of application Serial No.

690,330, September 21, 1933, 2,165,229, dated July 11, 1939.

now Patent No. Divided and this application November 28, 1940, Serial No.

1 Claim- (Cl. 179-1715) This invention relates to the signalling art and pertains especially to the transmission of intelligence from one geographically separated point to another by the use of phase modulated waves or carrier energy. This application is a division of my United States application #233,539, filed October 6, 1938, Patent No. 2,250,296, July 22, 1941, the latter being a division of my United States application Serial No. 690,330, filed September 21, 1933, now United States Patent 412,165,229, dated July 11, 1939.

An object of my present invention is to provide a new and useful system for producing a phase modulated wave of substantially constant frequency and amplitude. To do so, I provide an arrangement and a method wherein two carrier fequency voltages of substantially like frequency are combined less than 180 degrees out of phase, or any multiple of less than 180 degrees out of phase, to produce a resultant voltage. According to my invention, the phase of the resultant voltage is varied at signal frequency by varying the relative values of the voltages .combined at a signal frequency rate and an amount proportional to the amplitude of the signal frequency, limited, of course, by the phase shift referred to above imparted to the two portions of the carrier. The voltages may be phase shifted and amplitude modulated before combining or amplitude modulated and then phase shifted before combining.

Any amplitude modulation caused'in the re- As required by law, my present invention is defined with particularity in the appended claim. However, it may best be explained both as to its 1 structural organization and mode of operation by referring to the accompanying drawings wherein:

Fig. l is a wiring diagram of a phase modulation transmitting system disclosed and claimed in sultant phase modulated wave may be eliminated by limiting the resultant energy. To do so, the energy may be passed through electron discharge devices operated at their saturation point.

More specifically, according to my present invention, I carry out the foregoing objects by introducing in the circuits of a pair of electron discharge devices voltages of like frequency a predetermined number of degrees out of phase such that the phase difference is not 0, 180", or any whole multiple of 180, although phase .differences varying slightly from 0, 180, etc., are suitable. The outputs of the devices are so combined that there is a resultant voltage of like frequency. To vary the phase of this resultant voltage, or, in other words, the phase 'of the resultant carrier energy, I vary oppositely the internal impedancesof the electron discharge devices. The present invention relates to improvements in phase modulators of the type disclosed in my United States application Serial No.

" 588,309, filed January 23, 1932, now United States Patent #2,081,577 dated May 5, 19 39.'

my above-mentioned divisional application;

Figs. 2 and 3 are vector diagrams given in order to explain the operation of the system shown in Fig. 1; while,

Figs. 4, 5, and 6, inclusive, are wiring diagrams of modified phase modulators arranged in accordance with the present invention.

Turning to Fig. 1, illustrating a transmitter for transmitting phase modulated energy, carrier energy or potentials from an oscillation generator 2 are fed to the primary winding of a transformer 4, the secondary winding of which is symmetrically divided and connected as shown to the control grids of two discharge devices VI and V2. The generator 2 may be a crystal controlled oscillator, or any other form of substantially constant frequency oscillation generator. The oscillations from 2 are applied in phase opposition to the control grids of VI and V2. Biasing potentials for the control grids of VI and V2 are supplied from the source G connected as shown.

.The anodes of tubes VI and V2 are connected, as shown, through tuned circuits l0 and I2, respectively, and a source of anode potential 13 to the cathodes of, said tubes, which are connected together, as shown. The anodes of tubes Vi and V2 are also connected, as shown, by way a source G2 connected, as shown, by way. of resistances RI and R2 to the control grids of tubes l4 and' Hi, respectively. The point of connection between the resistances RI andR2 is connected, as shown, by way of a condenser l5 to the terminal of the source B. The anode electrodes of tubes l4'and I6 are connected together and to the cathodes by way of an inductance l8 and a direct-current source. The inductance l8 may form the primary winding of a transformer T, the secondary winding of which may be connected to a utilization circuit.

The tuned circuits [0 and I2 serveas plate impedances of the coupling tubes and also as phase adjusters to adjust the phase of the amplified carrier fed to the grids of the modulator tubes immofmmlflplicr.

l4 and I6, respectively. By tuning one of these tuned circuits, for example, ID, on the inductive side of resonance, and the other of the tuned circuits, as, for example, l2, on the capacitive side of resonance, the phase of the voltage applied to the grid of one of the tubes I4 and I8, is made lagging and to the other leading. Adjustment for a 45 lag and 45 leadwill make a total phas difference of 90 difference.

multiple of 90, so that 270 is equally as eflec-- tive as 90. This has been explained in considerable detail in United States application No.

588,309, filed January 23, 1932, now Patent go.

#2,081,577, dated May 25, 1937.

The vectorial relationship of the voltages in circuits l0 and I2 is illustrated in Fig. 2 for the particular cas of 90 separation where Ea illustrates the voltage in circuit l0 and Eb indicates the alternating voltage in circuit l2. These voltages are applied, as shown, to the control grids of tubes I4 and Hi to be amplified therein and consequently in the output circuit I8 of tubes I4, l6 there appears voltage Er, as shown in Fig. 2. This is a resultant voltage which is of a frequen'cy equal to the frequency of the voltage applied from source 2.

By oppositely varying the output of each of the two electron discharge devices l4, IS, the

' amplifier 26 is fed as indicated in opposite phas to the screen grids 23, 30 of tubes l4, l8. Cone sequently, the internal impedances of tubes I4 and II are varied oppositely and, as a result,

their'outputs are varied inversely to their internal impedances, thereby causing a phase shift of the resultant energy appearing in the output circuit l8 of the tubes. The phase modulated eriergy so appearing in the output circuit l8 of Other arrangements may be used for obtaining the phase shift and for differentially applying the modulating potentials. For example, an arrangement as shown in Fig. 4 may be used. In this arrangement carrier frequency oscillations from the source 2 are applied directly by way of transformer 30 to the control grid 3| of a thermionic tube and by way of a phase shifter 36 and transformer 32 to the control grid 33 of a thermionic tube 38. The phase shifter may 1m; part to the carrier frequency oscillations applied to the grids of tubes 38 and 43 the desired relative phase shift, which may be 90, or any desired amount less than 180. The phase shifted oscillations appear in th inductance l8, con- .nected, as shown, with the anode electrodes of 'both tubes. The inductance I8 is the primary winding of a transformer T and by the transformer action voltage is applied from said inductance to a utilization circuit 34 by way of a device 32 described hereinbefore.

I In the arrangement of Fig. 4 the modulating potentials are supplied from the source 24 by way of a modulating transformer 35, in phase opposition to the control grids 33 and 3| of tubes 38 and 40. The modulating potential transformer has its secondary winding connected in series with the radio-frequency input circuits of the tubes 38 and 40, as shown. The modulating potentials are applied differentially in series with the carrier voltages on the grids of tubes 38 and 40. The impedances between the anodes and cathodes of the tubes 38 and 40 are non-linear I and are obtained by operating the tubes on the electron discharge devices I4, l8 may then be I amplitude limited, and/or frequency multiplied, and/or amplified by a suitable device in 32 and .the greatest amount of phase shift possible with the scheme so far described is a value less than square law part of their characteristics.

The modulating potentials applied difierentially to the control grids of tubes 38 and 40 determine which of the two tubes supplies the most energy to the inductance l8, and therefore determine which tubecontrols to the largest extent the output energy, and thereby the phase of the energy, applied to the load.

Where plate modulation is preferable, an arrangement as shown in Fig. 5 may be utilized. This arrangement is substantially the, same as the arrangement of Fig. 4, described hereinbefore. In the arrangement of Fig. 5, however, eachanode circuit includes an output inductance and a portion of the secondary winding of the modulation transformer 35, as shown. 'Ihe output inductance comprises the primary of a transformer T2. The direct-current supply source is connected between the electrical center of the secondary winding of the modulation frequency transformer 35, and \the' cathodes of the tubes 38 and 40, as shown. The phase shifted waves are differentially modulated in tubes 33 and 40, and in particular in the anode circuits thereof, and are impressed therefrom on to the secondary winding of the transformer T2. The coupling between the primary winding of T2 and the secondary winding is preferably variable in order to insure that each tube in turn sup- 180, or with 90 phase displaced voltages, 90;

and it is also evident that thisarrangement in.- troduces a'small amount of amplitude modulation. To eliminate the amplitude modulation a thermionic relay device in 32 may be operated at all times at its saturation point. To increase or augment the relative amount of phase modulation, theapparatus 32 may include also some plies like amounts of energy to the secondary winding and from said winding to the utilization circuit 34 by way of the devices in 32.

In the arrangement of Fig. 6, a combination of screen grid and anode modulation is used.

In this arrangement the phase shifted oscillations are supplied to the control grids 33 and 3| of-the tubes 50 and n, the input electrodes of ment the screen grid electrodes 56and 51 of tubes 50 and 52 are connected, as shown, by way of resistances R4 and R5 to the terminals of the anode windings of transformer T2, as shown, and to the terminals of the secondary winding of the modulation frequency transformer 35. In other words, the resistances R4 and R5 are connected in series with the two halves of the sec-. ondary winding of the modulation frequency transformer between the screen grids and cathodes of the tubes 50 and 52. The inductances which form the primary windings of the transformer T2 are connected in a similar manner between the anodes and cathodes by way of the two portions of the secondary winding in the modulation frequency transformer.

The manner in which differential modulation is accomplished here by both the screen grids and the anodes will be better understood when it is realized that the anode to cathode impedance of each tube is, in a sense, in parallel branches of a circuit, a common portion of which includes a portion of the secondarywinding of the modulation frequency transformer. By combining the two types of modulation in this manner, a more linear modulation characteristic is obtainable, especially when screen grid tubes'are used.

What is claimed is:

In a phase modulation system, a source of wave energy of carrier wave frequency, a source of modulating potentials, a pair of electron discharge devices each having an anode, a cathode, an auxiliary grid and a control grid, a first transformer having a secondary winding coupled to the control grid and cathode of one of said devices, said transformer having a primary winding coupled to said source of wave energy, a phase shifter having an input coupled to said source of wave energy, said phase shifter having an output, a second transformer having a primary winding coupled to the output of said phase shifter, said second transformer having a secondary winding coupled to the control grid and cathode of the other-of said devices, transformer means coupling said source of modulating potentials differentially to the auxiliary electrodes of said devices and to the anodes of said devices, anda load circuit coupled to the anodes of said devices.

MURRAY G. CROSBY. 

